# ---
# title: 380. Insert Delete GetRandom O(1)
# id: problem380
# author: Tian Jun
# date: 2020-10-31
# difficulty: Medium
# categories: Array, Hash Table, Design
# link: <https://leetcode.com/problems/insert-delete-getrandom-o1/description/>
# hidden: true
# ---
# 
# Implement the `RandomizedSet` class:
# 
#   * `bool insert(int val)` Inserts an item `val` into the set if not present. Returns `true` if the item was not present, `false` otherwise.
#   * `bool remove(int val)` Removes an item `val` from the set if present. Returns `true` if the item was present, `false` otherwise.
#   * `int getRandom()` Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the **same probability** of being returned.
# 
# **Follow up:** Could you implement the functions of the class with each
# function works in **average** `O(1)` time?
# 
# 
# 
# **Example 1:**
# 
#     
#     
#     **Input**
#     ["RandomizedSet", "insert", "remove", "insert", "getRandom", "remove", "insert", "getRandom"]
#     [[], [1], [2], [2], [], [1], [2], []]
#     **Output**
#     [null, true, false, true, 2, true, false, 2]
#     
#     **Explanation**
#     RandomizedSet randomizedSet = new RandomizedSet();
#     randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully.
#     randomizedSet.remove(2); // Returns false as 2 does not exist in the set.
#     randomizedSet.insert(2); // Inserts 2 to the set, returns true. Set now contains [1,2].
#     randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly.
#     randomizedSet.remove(1); // Removes 1 from the set, returns true. Set now contains [2].
#     randomizedSet.insert(2); // 2 was already in the set, so return false.
#     randomizedSet.getRandom(); // Since 2 is the only number in the set, getRandom() will always return 2.
#     
# 
# 
# 
# **Constraints:**
# 
#   * `-231 <= val <= 231 - 1`
#   * At most `105` calls will be made to `insert`, `remove`, and `getRandom`.
#   * There will be **at least one** element in the data structure when `getRandom` is called.
# 
# 
## @lc code=start
using LeetCode

## add your code here:
## @lc code=end
